The present invention relates generally to a method for controlling creep torque in a vehicle.
Automotive vehicles typically have a vehicle technical specification that defines how fast the particular vehicle should accelerate from a stop when it is idling in gear and the driver applies no pressure to the brake pedal or the accelerator pedal. To accomplish this, the powertrain system is designed to apply a specific amount of torque when the vehicle is stopped, called creep torque. This creep torque, then, acts against the brake application by the driver while the vehicle is stopped. Upon release of the brake pedal, the vehicle will begin to move, even without pressing on the accelerator pedal. In a vehicle with a conventional internal combustion engine, automatic transmission and torque converter, applying a creep torque is relatively easy since the engine is operating all of the time—even while the vehicle is stopped at a traffic light.
For some newer types of vehicles where an engine is not operating all of the time, applying creep torque is more of a challenge. Such vehicles may be, for example, two-mode hybrid vehicles, battery electric vehicles, and fuel cell vehicles. For these types of vehicles, when the vehicle is stopped (while in gear) the electric motor is typically operated to supply a creep torque similar to conventional vehicles. In this way, drivers switching between driving conventional vehicles and these newer types of vehicles will get the same sensation when releasing the brake to start-up from a stop. However, the extra energy used by the motor to maintain the creep torque while the vehicle is stopped while in gear somewhat defeats the purpose of implementing these non-conventional powertrains in the new types of vehicles.